Propeller control system



Oct. 11, 1960 BRANDES ETAL 2,955,663

PROPELLER CONTROL SYSTEM Filed Dec. 11, 1956 INVENTORS E0 v I?!Ben/v0.5.5 y P/CH'A'RDA H1250 Afar/2M ATTORNEY A 2,955,663 PRQPELLERCONTROL SYSTEM Roy H. Brandes, Dayton, and Richard A. Hirsch, WestMilton, Ohio, assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Filed Dec. 11, 1956, Ser. No. 627,619

'15 Claims. (Cl. 170-'160.21)

This invention pertains to propellers, and particularly to an improvedcontrol system for a variable pitch propeller designed for use with agas turbine engine.

Heretofore, the tendency of the blades of a variable pitch propeller tomove in the decrease pitch direction toward a low angle, or flat pitchposition, due to the aero- "dynamic and centrifugal twisting momentforces acting on the blades, has been troublesome. Thus, in previouspropeller control systems, means were included to control and limit therate of pitch change in the decrease pitch direction. The aforesaidmeans necessarily increases the complexity of the propeller controlsystem, but were considered essential from the safety standpoint.However, in a variable pitch propeller having a mechanical pitch lock, amechanical low pitch stop, and safety feathering means, the problem ofcontrolling the rate of pitch change in the decrease pitch direction isof little, or no, significance. Therefore, the propeller control systemcan be simplified. Accordingly, among our objects are the provision ofan improved control system for a variable pitch propeller; a furtherprovision of a variable pitch propeller control system including safetyfeathering means; and the still further provision of a variable pitchpropeller control system having governor valve means and a featheringvalve means including means for automatically disabling the governorvalve means upon operation of the feathering valve means.

atent ICC the torque units so as to increase or decrease propellerPitch. The distributor valve is controlled by governor valve means whichmaintain propeller speed substantially constant during the propelleroperation in the governing regime. Moreover, during the operation in thegoverning regime, the pitch change rate is proportional to the amount ofoff speed. The governor valve can also be manually positioned to operatethe propeller in the manually selected blade angle regime and theemergency feathering'regime. The control system also includes afeathering valve assembly which is operable to disconnect the highpressure fluid supply to the distributor valve thereby rendering thegoverning means ineffective during manual feathering, safety feathering,and automatic feathering operation. At this time, the feathering valveassembly connects the high pressure supply directly to increase pitchchambers of the torque units while connecting the decrease pitchchambers to drain so as to move the propeller blades to the runfeathered position.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of the present invention isclearly shown.

The'drawing is a schematic diagram on the propeller I control system ofthis invention.

The aforementioned and other objects are accomplished in the presentinvention by having a single high pressure supply conduit for thegovernor operated distributor valve which conduit can be cut off fromthe source of high pressure fluid during operation of the featheringvalve means. Specifically, the invention relates to an improved controlsystem for a variable pitch propeller of the type disclosed in FrenchPatent 1,173,259, which corresponds to copending application Serial No.572,348, filed March 19, 1956, and assigned to the assignee of thisinvention.

Thus, the propeller includesa hub having a plurality. of 1 fluidreservoir containing 'suflicient fluid to completely feather thepropeller under all conditions.

Thepitch position of the propeller blades is adjusted by fluid pressureoperated motors, or torque units, carried by the propeller hub. Theregulator reservoir contains a quantity of fluid, such as oil, andcarries a plurality of pumps, which are energized incident to thepropeller rotation, for drawing fluid from the reservoir and deliveringthe fluid under high pressure to a hydraulic control system. Thehydraulic control system includes a With particular reference to thedrawing, the propeller includes a' hub 10 shown schematically in thedrawing. As is conventional, the hub 10 includes a plurality of radiallyextending sockets, such as the one indicated by numeral'll in thedrawing. A propeller blade 12 is journalled for rotation about itslongitudinal axis by means of bearings 13 within the socket 11. Thepropeller blade is shown schematically in the drawing and, thus isshownincluding an integral cylinder 14 having internal helical splines 15. Apiston 16 is disposed for reciprocal movement within the cylinder 14,the piston 16 having external helical splines 17 which mate with theinternal helical spline 15 of the cylinder 14. In addition, a piston 16has internal integral helical splines, not shown, which mate withexternal helical splines on a reaction member 18 which is integral withthe hub 10. Thus, it will be appreciated that upon reciprocation of thepiston 16, rotation will be imparted to the propeller blade 12. In

addition, upward movement of the piston 16, as shown in the drawing,will move the propeller blade 12 in the increase pitch direction, andvdownward movement of the piston 16 moves the propeller blade in thedecrease pitch direction.

'Ihe propeller blade is shown integral with a bevelt'ype sector gear 19which meshes with a bevel-type master gear 20 supported for rotation inthe hub 10 about the horizontal propeller axis. It is to be appreciatedthat each propeller blade 12 has a bevel-type sector gear meshing withthe master gear 20, and the function of the master gear 20 is tocoordinate and synchronize the pitch adjustment movement of all thepropeller blades mounted in the hub.. Thus, it will be appreciated thatthe master gear has a predetermined angular position for each and everypitch position of blades 12. In accordance with the teachings of BritishPatent 798,372, which corresponds to copending application Serial No.571,523, now Pat. No. 2,882,975, filed March 14, 1956,

in. the name of Richard 'A. Hirsch et al., and assigned 7 to theassignee of this invention, the master gear 20 has associated therewitha mechanical pitch lock designated 4 generally by the numeral 21 and amechanical low pitch distributor valve for directing the high pressurevfluid. to l stopdesignated, generally by the numeral 22. Theconstruction of the mechanical pitch lock and the mechanical pitch stop,per se, constitute no part of this invention. However, the functionalrelationship of these safety devices. to the propeller control system iswithin the scope of this invention. It suflices to say that themechanical pitch lock 21 is moved into the operating position by aplurality of springs 23 so that the nonrotatable ratchet teeth 24thereof engage a series of ratchet teeth 25 formed integral withthe'master gear 20. When the ratchet teeth 24 engage the ratchet teeth25 rotation of the master gear in the decrease pitch direction isprecluded, although rotation of the master gear in the increase pitchdirection is permitted due to the ratchet teeth construction. Themechanical pitch lock is normally maintained in the release position bythe application of fluid under pressure to servo chamber 26.

The pitch stop 22 includes a flange element having a plurality ofcircumferentially spaced lugs 27 thereon which rotate with the mastergear 20. The lugs 27 can be engaged by a set of complementary,nonrotatable lugs mounted on an axially movable member 28. The member'28 is engaged by the springs 23 which normally position the lugs of themember 28 in the path of movement of lugs 27. The low pitch stop can bereleased to permit movement of the blades to a negative pitch positionby the application of fluid under pressure to servo chamber 29.

As alluded to hereinbefore, the major components of the hydrauliccontrol system are disposed within a regulator assembly rotatable withthe propeller hub. The propeller control system includes a plurality ofpumps 30 which are driven incident to the propeller rotation, and areoperable to draw fluid from the rotating reservoir and supply the fluidunder pressurethrough check valves 31'to high pressure conduit 32. Thehigh pressure conduit 32 communicates with a constant speed, or governorvalve assembly, 40 and also with a check valve 33 of the feathering pumpand reservoir assembly 34 which is connected to and rotatable with thehub. The propeller control system also includes a feathering valveassembly designated generally by the numeral 35, a solenoid valveassembly designated generally by the numeral 36, and a pitch stop andpitch lock valve assembly 37. High pressure conduit 32 communicateswithport 38 of a pressure reducer valve designated generally by thenumeral 39. The pressure reducer valve 39 includes a plunger 41 which isbiased downwardly as viewed in the drawing by means of a spring 42. Itis to be understood that all of the components in the regulator, namelyvalve assemblies 35, 36, 37 and 40 are subject to centrifugal force inthe direction of arrow 4201. Land 42b on the plunger 39 controls athrottling port for .43, which is connected at one side through arestriction 44 to the bottom of the plunger, namely, servo chamber 45.The plunger land 42b throttles the flow of high pressure fluid throughport 43 and maintains substantially constant pressure in conduit 47 andpassage 46 which pressure may be on the order of 400 psi. The lowpressure servo conduit 47 communicates with the pitch lock and pitchstop assembly 37 as shown in the drawing. The low pressure passage 46communicates with a speed sensitive valve unit designated generally bythe numeral 48.

The speed sensitive valve unit 48 comprises a reciprocable sleeve 49which is biased upwardly by means of a spring 50a. Within the sleeve isa speed sensitive plunger, or piston 50. The piston 50 is subject to thethrust of centrifugal force in the direction of arrow 42a, and a thrustof centrifugal force tends to move the piston 50 upwardly as viewed inthe drawing. The lower end of the piston 50 is connected by means of apin 51 to a lever 52, the other end of which is pivoted at 53 to thehousing of the valve assembly 40. The lever 52 and the piston 50constitute a substantial mass responsive to centrifugal force. The lever52 is engaged by a spring 54 between the pivot points 51 and 53 and thespring 54 opposes movement of the piston 50 and lever 52 under thethrust of centrifugal force. The piston 50 includes a control land 55which cooperates with a series of ports 56. The land 55 connects, ports56 either. to the low servo pressure through the passage 46, or todrain. The ports 56 connect with a passage 57 which communicates with aservo chamber 58 at the lower side of a distributor valve plunger 59.

The distributor valve plunger 59 is positioned hydraulically, and thusincludes a differential area piston 60, having a lower areasubstantially twice the size of the upper area. The upper, or smallerarea of the piston 60 is continuously subjected to the low pressurefluid from passage 46. The servo chamber 58'is alternately connected todrain and to pressure by means of a land 55 of the speed sensitivepiston 50, and thus, the position of the distributor valve plunger 59can be controlled. In addition, to maintain the requisite sensitivity,the pressure in servo chamber 58 is cyclically pulsed by a mechanicallyactuated jitter plunger 61, controlled by a cam 62 and having a conduit63 connected with the servo chamber 58.

The distributor valve plunger 59 is connected to a lever 64 havingintermediate pivot point 65 on the housing of the valve-assembly 40. Oneend of the lever 64 ispivotally connected to the plunger 59 and theother end of the lever 64 is pivotally connected to the sleeve 49. Thisarrangement constitutes a closed loop servo'system inasmuch as movementimparted to the distributor valve plunger causes a follow-up movement ofthe sleeve 49 relative to the originaldisplacement of the speedsensitive piston .50 so that the rate of change of propeller pitch ,isproportional to the amount of off speed. This arrangement accomplishesproportionalized speed governing. The distributor valve plunger 59includes space lands 66, 67 and 68. An internal passage 69 is formed inthe plunger 59 for interconnecting the annular grooves between lands 66,and 67 and the annular groove between lands 68and the piston 60. Theannular groove between thelands 66 and 67 communicates with a highpressure supply port 70. This high pressure supply port communicateswith conduit 71, which also communicates with the. inlet port 72a of thesolenoid valve assembly 36. In addition, the conduit 71 communicateswith a passage 72 in the feathering-valve assembly 5. The passage 72connects with a minimum pressure valve element 73, constituting theplunger 74 which is biased downwardly by means of a spring 75. The highpressure trunk line, or conduit, 32 communicates with a passage 76 ofthe feathering valve assembly 35 and thence to a port 77 of a shuttlevalve 78. With the shuttle valve 78 in the position depicted in thedrawing, the port 77 communicates with a port 79 and the bottom side ofthe minimum pressure valve plunger 74. In addition, the port 79communicates through a branch passage to the annular groove between thelands on the plunger 74. Thus, when the pressure in conduit 32 exceedsthe setting of the minimum pressure valve 74, high pressure fluid willbe .spppliedto passage 72 and conduit 71 and thence to the 'supplyportsof the distributor valve.

he distributor valve land 67 controls an increase pitch port whichcommunicates with conduit 80. The distributor valve land '68'controlsthe decrease pitch port whiclrcommunicates with conduit 81. Conduits 80and '81communicate respectively with increase and decrease pitchchambers 82 and 83 of the torque units. The annular'groove between land67 and 68 communicates with a drain port 84 which connects with adrainconduit 85. Thus, when the distributor valve plunger 59 moves upwardly,the increase pitch conduit 80 is connected to the drain conduit 85, andthe decrease pitch conduit 81 is connected to the high pressure conduit71. Conversely when the distributor valve plunger 59 moves downwardly,the increase pitch conduit is connected to the high pressure conduit 71,and the decrease pitch conduit is connected to the drain conduit 85.

The'increase pitch conduit'80 includes, or connects with, abranchconduit 86 which connects with a servo chamber 87 associated'with apressure control valve 88.

The pressure control valve 88 includes aplunger which is biased upwardlyby means of a spring 89. -The upper surface of the plunger is subjectedto the pressure potential in the high pressure conduit 71 throughpassage 90. Thus, the pressure control valve regulates the pressurepotential available for varying propeller pitch. More particularly, thepressure control valve 88 assures that the pressure potential availablefor increasing propeller pitch will always exceed the demands of thepitch changing motor. Thus, when high pressure fluid is supplied toconduit 80, it is likewise applied to the servo chamber 87. This highpressure fluid in servo chamber 87 assists the spring 89 .in urging theplunger upwardly so as to close drain port 92. ,The pressure fromconduit 71 acts in opposition to the force of spring 89 in servo chamber87. Thus the pressure control valve will always assure that therequirements of the pitch changing motor during movement in theincreased pitch direction will be maintained. l

Particular attention is called to the fact that high pressure fluid isemployed 'b0th to increase and decrease propeller pitch. Thisarrangement enables simplification of the propeller control system, andthis arrangement is only permissible since the propeller assemblyincludes safety devices hereinbefore alluded to. Thus, since thepropeller includes a mechanical pitch lock, a mechanical low pitch stop,and a hydraulic low pitch stop to be described, the necessity forcontrolling the rateof decrease pitch change has been eliminated.

As seen in the drawing, the feed-back gear 20 includes a toothed flange92a. More particularly, the flange 92a is partially toothed and isengaged by a pinion gear 93 which is connected to a rotary feed-backshaft 94. During a predetermined movement of the propeller blades, thepinion gear 93 engages the toothed portion 92a of the flange so as torotate the shaft 94. This feed-back shaft 94 is actually only rotatedduring movement of the blade from the full reverse to a predeterminedpositive angle, for instance a positive 32.. The feedback shaft 94extends into the regulator and is formed with a high lead screw 95. Thehigh lead screw engages a nut 96 which is articulated to one end of alever 97 having an intermediate pivot point 98. The other end of thelever 97 is articulated to a rod 99 which connects with a control shoe100. The intermediate pivot point 98 is connected to a rod 101, the endof which carries a roller 102 which cooperates with a cam surface 103formed on the lever 52. In the governing range, when the blades reach apredetermined low angle, for instance 'a positive 20, the rotaryfeed-back shaft 94 will position the lever 97 by pivoting the same in aclockwise direction about its articulated connection with the rod 9 9soas to move the rod' 101 to the right so that the roller 102 will engagethe cam surface 103 at the end and move the piston 50 upwardly. By sodoing, the flow of hydraulic fluid to the pitch changing motor in thedecrease pitch direction is interrupted thereby establishing a.hydraulic low pitch stop.

Moreover, in accordance with the teachings of the aforementionedcopending application Serial No. 572,348, the position of the hydrauliclow pitch stop, or in other words the angular position of the propellerblades 12 at which the hydraulic low pitch stop becomes effective, canbe varied through a beta follow-up system. The beta follow-up systemincludes the rod 99 which is connected 'to the control shoe 100, thecontrol shoe 100 riding on a control ring 104. It is to be appreciatedthat the control ring 104 forms a part of the stationary adaptorassembly about which the regulator. rotates. Thus, the shoe 100 rotatesabout the control ring 104, and upon axial movement of the control ring104 axial movement will be imparted to the rod 99. The control ring 104is connected by a plurality of high lead screws, indicated by numeral105, to a segmental internal ring s .107, t m dm cc it onw r g r,..2y-.Pi11 a gears 106. The condition. control gear has a radial abutment108 extending therefrom which is. connected to the pilots power lever.The regulator'also includes a feathering control ring 109 and a speedsynchronizing ring 110. The feathering control ring is connected'by aplurality of high lead screws designated by the numeral 111 to a piniongear 111a which meshes with a feathering control gear 112. Similarly,the speed or synchronizing control ring is connected by a plurality ofhigh lead screws designated by the numeral 113 to a pinion gear 114which meshes with synchronizing control gear 115. Both control gears 112and 115 have radial abutments extending therefrom through which they mayberotated.

The condition control ring 104 also has control shoes 116 and 117thereon. Control shoe 116 is connected to a rod 118 while control shoe117 is connected to a rod 119. The rod 118 is pivotally connected to acrank arm 120 for actuating a selector valve 121a. Therod 119 is formedwith three discrete cam surfaces 121, 122 and 123. The control ring 110receives a control shoe 124 which is connected to a rod 125 having aroller 126 thereon. The roller 126 cooperates with the cam surface 127of a lever 128. The lever 128 has an intermediate pivot at 129 to thecasing of valve assembly 40 and the free end thereof engages a combinedspring retainer and servo piston 130 for the governor spring 54.

The feathering control ring 109 has a control shoe 131 thereon which isconnected to a rod 132 having cam surfaces 133 and 134. The cam surfaces133, 134, 121, 122 and 123 coact with a pair of cam followers 135 and136 mounted on a trolley 137 pivotally connected at 138 to a featheringtrigger valve plunger 139.'. The plunger 139 is biased downwardly bymeans of a spring 140, and has a pair of spaced lands 141 and 142. Theannular groove between lands 141 and 142, is always in communicationwith the high pressure passage 76. The land 141 controls a port 143which is connected with a servo chamber 144 associated with the shuttlevalve 78. The shuttle valve 78 includes a plurality of spaced lands 145,146, 147 and 148 and 149. The shuttle valve 78 is biased upwardly bymeans of a spring 150. With the shuttle valve 78 in the positiondepicted in the drawing, land 146 blocks communication between ports 151and 152, the annular groove between 147 and 148 interconnects passages76 and 79, and the annular groove between lands 149 and 148interconnects passages 153 and 154. Under these conditions high pressurefluid is supplied to conduit 71 and the increase pitch conduit 80communicates with the increase pitch chambers ,82

through passages 153 and 154.

The feathering control valve assembly 35 also includes a decrease loadervalve which constitutes a spring biased check valve. Since the pumps 30normally pro; duce excess flow, the pressure control valve 88 suppliesthis excess flow to the controlled drain line 85. The controlled drainline 85 communicates with the top side of the decrease loader valve 155.The bottom side of the decrease loader valve 155 communicates'with port151 and the conduit 156 which communicates with the decrease pitchconduit 81. Thus the decrease loader maintains a predetermined pressureat all times in the decrease pitch conduit 81 and in the decrease pitchchambers 83 as set forth more specifically in theaforementionedcopending applications. However, when the shuttle valve 78is moved downwardly by pressure fiuid acting on the land 145, conduit156 is connected to drain through ports 151 and 152, and the connectionbetween passages 153 and 154 is interrupted. In addition, the connectionbetween passages 76 and 79 is interrupted thereby interrupting thesupply of high pressure fluid to the conduit 71 and the inlet port 70 ofthe distributor valve 59. Thus, when the trigger valve 139 is movedupwardly, the shuttle valve is moved downwardly to disconnect the dis-;tributor valve 59 and the speed system or governor valve 50 :fromcontrolof the pitch changing motors. Moreover, at this time the passage76 is connected directly to the passage 154 and thus high pressure fluidis supplied directly to the increased pitch chambers 82, while thedecrease pitch chambers 83 are connected to drain through conduit 81,conduit 156, port 151, and port 152. Consequently, the propeller blades12 will move to their feathered position.

The trigger valve 139 can be moved upwardly by either movement of rod132 or rod 119. Thus, if the rod 132 is moved to the left as viewed inthe drawing due to move ment of the feathering control ring 109 to theleft, the roller 136 will engage the cam surface 134 thereby movingvalve plunger 139 upwardly to interconnect passage 76 and port 143.Similarly, the rod 119 can be moved to the right so that the roller 135engages the cam surface 121 thereby moving the plunger 139 upwardly.However, when the rod 119 is moved to the left so that the roller 135engages the cam surface 123, movement of the rod 132 to the left so thatthe roller 136 engages the cam surface 134 will not impart sufficientmovement to the trigger valve 139 to actuate the shuttle valve 78. Thisis known as the feathering block-out during operation in the manuallyselected blade angle regime, or beta range.

The feathering control ring gear 112 is used to initiate all normalfeathering operations, and, thus, may be actuated manually during manualfeathering, automatically during takeoff due to automatic featheringmechanism, or automatically during operation in the governing regimewhen the aircraft is in flight due to a negative torque signal sensingmechanism, as set forth in the aforementioned copending application S.N.572,348. In addition, the condition control ring gear 107 can beactuated to call for emergency feathering by rotating the gear 107 inthe clockwise direction as viewed in the drawing. By this movement, therod 118 and the rod 99 are simultaneously moved to the right as viewedin the drawing, the rod 99 actuating the roller 102 through the link 97and the rod 101 to cam the piston 50 upwardly so as to call for anincrease in propeller pitch. At the same time, the rod 119 is moved tothe right so that the roller 135 engages the cam surface 121 therebymoving the trigger valve 139 upwardly to actuate the shuttle valve 78and call for an increase in propeller pitch. Thus, under emergencyfeathering conditions, if for some reason the feathering valve assembly35 shauld be inoperative, feathering can be accomplished through thegovernor valve and distributor valve plunger 59.

The only way in which the feathering valve assembly 35 can be renderedinoperative is by failure of the shuttle valve 78 to move from theposition it is shown in the drawing wherein ports 77 and 79 areinterconnected, and passages 153 and 154 are interconnected, downwardlyto a position where the connection between ports 77 and 79 is blockedand the connection between passages 153 and 154 is blocked so that port77 is connected to passage 154. This inoperativeness could be caused bya failure in the trigger valve 139, since the trigger valve 139 controlsthe application of fluid under pressure to servo chamber 144 for movingthe shuttle valve 78 downwardly against the force of spring 150. Sincethe shuttle valve 78 only has two positions, as shown in the drawing,namely, one wherein it connects the source of fluid under perssure tothe supply port of the servo distributor valve 59, and a second whereinit connects the source of fluid pressure directly with the increasepitch chambers of the pitch adjusting motor, if the shuttle valve 78does not move from the position shown in the drawing to a position whereport 77 is connected with passage 154 upon actuation of the triggervalve 139 during emergency feathering, fluid under pressure will beapplied to the increase pitch chamber of the pitch adjusting motorby theservo distributor valve 59.

Automatic feathering during take 011 constitutes a safety mechanism fora multipower plant aircraft. As shown in the aforementioned copendingapplication S.N. 572,348 the feathering control ring gear 112 ispositioned by a solenoid which is automatically energized upon failureof an engine during take off to feather the propeller of the failingengine. The solenoid for actuating the feathering control ring gear 112can also be energized automatically by a negative torque signalmechanism when the aircraft is airborne, as well as by a manual switchcontrolled by the pilot.

The speed sensitive plunger 50 in combination with the lever 52 and thespring 54 constitute an isochronous governor assembly. That is, thegovernor assembly tends to maintain propeller speed substantiallyconstant at a predetermined value. However, the force of the spring 54can be varied by movement of the lever 128 as effected by movement ofthe control ring which is actuated by the synchronizing ring gear 115.The synchronizing mechanism whereby the speed of the said propeller canbe synchronized with that of the master propeller by resetting thegovernor springs, constitutes no part of this invention.

The solenoid valve assembly 36 includes a casing having disposed thereina reciprocable plunger having space lands 161 and 162. The plunger 160also includes armatures 163 and 164. As is conventional practice, thesolenoid valve is normally spring centered by oppositely acting springs165 and 166. The land 161 controls a supply of high pressure fluid fromsupply port 72a through a pressure compensating valve assembly 167 to anincrease pitch conduit 168 which connects with a passage 153 of thefeathering valve assembly 35. The land 162 controls a port associatedwith a conduit 169 which connects with the decrease pitch conduit 81. Itis noted that the land 162 is of sufiicient width so that the conduit169 can never be connected to the high pressure conduit 71, but can onlybe connected to drain. Thus, when the plunger 160 moves to the right,conduit 168 is connected to drain through the compensating valveassembly 167 and the port controlled by land 161, while the fluidrequired for a decreasing propeller pitch is supplied by the decreasedloader valve 155. The solenoid valve plunger 160 is continuouslyreciprocated during operation in the governing regime. Control of thepropeller pitch is effected by varying the dwell in the open position ofthe plunger 160 so that the net flow to either side of the torque unitswill be such as to either increase or decrease propeller pitch.Energization of the windings 170 and 171 is controlled by an electronicunit, forming no part of this invention.

The pressure compensating valve assembly comprises a check valve 172which is connected in parallel with a pressure reducer valve 173, andwhich maintains a substantially constant pressure in chamber 174 so asto control the rate of flow from the increase pitch chambers to drainthrough the port controlled by land 161.

The pitch lock and pitch stop control valve assembly 37 includesinaddition to the rotary selector valve 121a, a mechanical low pitch stopcontrol valve 175, a mechanical pitch lock control valve 176 and a speedsensitive valve 177. These valve components are of the type disclosed inthe aforementioned copending application Serial No. 571,523, and per se,constitute no part of this invention. Suffice it to say that the speedsensitive valve 177 is calibrated to move upwardly at a speed somewhatabove the speed setting of the governor valve assembly. Thus, inresponse to a predetermined propeller overspeed, the valve 177 will moveupwardly thereby connecting the servo chamber above valve 176 to drainand permit the spring 180 to move the pitch lock control valve upwardly.When the control valve 176 is moved upwardly by spring 180, the passage181 is connected to drain through passage 182, and since the passage 181is connected-to conduit-183 which communicates with the servo chamber 26of the mechanical pitch lock, the springs 23 will move the ratchetelement 24 into engagement with the ratchet element 25 so as to preventfurther movement of the blades in the decrease pitch direction. Normallywhen propeller speed does not exceed a speed setting of the valve 177,the pitch lock is maintained released by the application of the lowpressure fluid from conduit 47 through passage 181 to conduit 183.

When the condition control ring gear 107 is moved in thecounterclockwise direction as viewed in the drawing, the control ring104 is movedto the left thereby moving the rod 118 to the left so as toturn the crank arm 120 whereby the selector valve plunger 121a will berotated in the counterclockwise direction so as to interconnect passage187a with passage 184 thereby moving the pitch stop control valve- 175downwardly against the spring 186. When the low pitch stop valve 175 ismoved downwardly, low pressure fluid from conduit 47 is admitted toconduit 187 and thence to the servo chamber surrounding the piston 130so as to reset the governor valve spring 54. Thus, by'resetting thegovernor valve spring 54 and lever 52 has its cam surface 103 maintainedin engagement with the roller 102. Hence, by moving the rod 101 byeither the rod 99 or by the feed-back shaft 94, the position of thepiston 50 can be controlled so as to select any desired blade angle inthe beta range. Simultaneously, low pressure fluid from conduit 47 isadmitted to conduit 188 and to the servo chamber 29' of the mechanicallow pitch stop to permit movement of the blades below a positive 18 andto the full reverse position.

As alluded to hereinbefore, the present invention also contemplates theuse of an electric motor feathering pump which is mounted in thefeathering pump and cooling reservoir assembly 34. The pump asdesignated by numeral 200 is driven by an electric motor 201 through amechanical connection indicated by a line 202. The controlled drain flowin conduit 85 is supplied to the reservoir. The reservoir 34 ismaintained under a slight pressure, i.e., 20 to 30 p.s.i. by having arestrictor 203 in the return line 209. This pressure is maintained inthe reservoir and the controlled drain line 85 for supplying thedecrease loader valve 155 and to prevent syphoning of the pitch lockrelease chamber and the pitch stop release chamber. In other words, someliquid is always present in the pitch stop and lock release chambers.

The regulator reservoir and the feathering pump reservoir areinterconnected by a conduit designated by the numeral 209, having arestriction 203, one end of the conduit 209 opening to the center of thereservoir 34 which rotates with'the propeller. Thus, the flow of fluidthrough conduit 209 can only be accomplished when the reservoir34 isfull of oil since the oil is normally thrown outward by centrifugalforce. However, the incoming pressure oil in conduit 85 will force thecool oil through the conduit 209 and back to the regulator reservoir.

This continuous circulation of oil prevents the oil from becomingdangerously hot.

In addition, the feathering pump 200 can be energized manually by thepilot and automatically under certain conditions such as duringautomatic feathering and feathering due to the negative torque signal.The feathering pump is used to supply fluid under pressure to adjust thepitch position of the propeller blade when. the propeller is notrotating. In addition, the pump 200 is used to supply pressure when thepropeller is rotating so slowly that the pumps 30 develop insuflicientpressure, for instance during the completion of the feathering movementof the blades 12. Thus the pump draws fluid from the reservoir 34, andthe outlet of the pump is connected to the check valve 33. The checkvalve 33 includes a plunger 210 having a sealing land 211 and a dampingland 212 which is perforated. The plunger 210 is biased by a spring 213and a sealing land 21 1 is exposed to the oppositely acting pressures inconduit 71 and the output of the pump 200. Thus, when the pressure inthe output of the pump 200 exceeds the combined force of the pressure inconduit 71 and the spring 213, it being remembered that centrifugalforce acts upwardly on the plunger 210, the outlet of pump 200 will beconnected to the high pressure conduit 32. In addition, the outlet ofpump 200 is connected by conduit 214 to a pressure control valve 215.The pressure control valve includes a centrifugally responsive plunger216 which is acted upon by the output pressure .of the pump 200 as wellas a spring biased centrifugally responsive valve 217.. The featheringpressure control valve 215 controls the output pressure of the pump 200,and since the centrifugally responsive element 217 is connected to thepressure control valve 216 through a lever 218, the pressure of the pump200 is proportion to the speed of the propeller rotation when thepropeller is rotating. That is, the pressure outputof the pump 200 isdetermined by the spring load on element 217 and centrifugal force whenthe propeller is rotating. ,However, when the propeller is stationarythe spring load on the element 217 alone determines the output pressureof the pump 200.

Operation of the propeller mechanism is substantially as follows. Duringoperation in the speed governing regime, propeller pitch is undercontrol of the distributor valve 59. Thus, during propellerover-speeding, the speed responsive piston moves upwardly to connectservo chamber 58 to drain, whereupon the constant low pressure acting onthe smaller area of piston 60 will move the distributor valve plunger 59downwardly. This downward movement of the plunger 59 will move thesleeve 49 upwardly through the link 64 in a follow-up relation so thatports 56 will be closed, by land 55. With the distributor valve 59 moveddownwardly, high pressure fluid from conduit 71 is supplied to theincrease line while the decrease pitch line 81 is connected to drain.Thus the pitch of the propeller blades will be moved in the increasedirection so as to reduce the over-speed.

Conversely when the propeller speed falls below the speed setting of thegovernor, the piston 50 will move downwardly thereby supplying lowpressure fluid through ports 56 to the servo chamber 58 and effectingupward movement of the distributor valve plunger 59. Upward movement ofthe plunger 59 will result in downward movement of the sleeve 49 in afollow-up manner so as to again close the ports 56. With the plunger 59moved upwardly the decrease pitch conduit 81 is connected to highpressure fluid while the increase pitch conduit 80 is connected to drainso that the propeller blades will move in the decrease pitch directionthereby permitting propeller to increase its speed.

When the trigger valve 139 of the feathering control valve assembly isactuated by either rod 132 or rod 119, the shuttle valve 78 interruptsthe supply of high pressure fluid to the conduit 71 thereby disablingthe distributor valve 59 and the governor valve. At this time, theincrease pitch chambers are connected directly to the output of thepumps through high pressure conduit 32 and the decrease pitch chambersare connected to drain. This feathering operation is used during manualfeathering, emergency feathering, automatic feathering, and negativetorque signal feathering. It should be pointed out that the negativetorque signal feathering mechanism is of the uncommitted type, whereasthe automatic, manual and emergency feathering systems are of thecommitted type. Emergency feathering means feathering by actuating thecontrol ring gear 107 to manually position the governor pilot valve andthe trigger valve of the feathering valve assembly. Thus, emergencyfeathering will only be used when the solenoid for actuating thefeathering control ring gear 112 is inoperative for any reason, such asa failure of the electrical power supply system of the aircraft.

In the beta range, the condition control ring gear 107 is manipulatedmanually by the pilot to position the roller 102 with respect to the camsurface 103, it being realized that the cam surface 103 is maintained inengagement with the roller 102 by virtue of increasing the load on thespring 54 through the piston 130 which is actuated by the fluidcontrolled by the rotary selector valve 121a. At this time, if the rod101 is moved to the left, thereby calling for a decrease pitch movementof the blades, the piston 50 will move downwardly so as to supply lowpressure fluid to the servo chamber 58 moving the distributor valve 59upwardly. This will cause the application of pressure fluid to thedecrease pressure chambers while the increase pitch chambers areconnected to drain. When the angle selected by the pilot has beenobtained by the blades, the feed-back mechanism comprising sector gear92, pinion gear 93, and the rod, or shaft, 94 will reposition the roller102 through rod 101 and link 97 so as to interrupt further applicationof pressure fluid to the torque units. Thus in the beta regime anyspecific angle between the full reverse angle and the low positive pitchstop angle of 20 can be selected by the pilot.

During emergency feathering, as alluded to hereinbefore, the rod 99 ismoved to the right thereby camming the piston 50 upwardly through link97, rod 101 and roller 102 so as to effect downward movement of thedistributor valve plunger 59. At the same time, the rod 119 is moved tothe right so as to effect upward movement of the trigger valve 139through the trolley 137, the roller 135 and the cam surface 121.However, if for some reason the shuttle 78 should fail to operate,nevertheless high pressure fluid will be directed to the increase pitchchambers of the torque units to increase propeller pitch by thedistributor valve 59. However, if the feathering control valve 35 isworking properly, the shuttle valve 78 will disable the governor valveby cutting off the supply of high pressure fluid thereto.

From the aforegoing it is readily apparent that the present inventionprovides a simplified hydraulic control system for a variable pitchpropeller, the simplification being possible by virtue of incorporatingthe various safe- -ty devices for preventing movement of propellerblades to a dangerously low angle upon a malfunction.

While the embodiment of the present invention as disclosed hereinconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure, first valve means operable to control said pitch adjustingmeans during propeller operation in the regimes of constantspeed and thebeta range, second valve means serially connected between said source offluid under pressure. and said first valve means and operable to controlsaid pitch adjusting means during feathering operation of saidpropeller, first means operable to actuate the second valve means toinitiate feathering operation of said propeller, manually operable meansfor selectingthe regime of propeller operation, and means operableduring propeller operation in the beta range for preventing actuation ofthe second valve means by operation of said first means.

-2. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure, first valve means operable to control said pitch adjustingmeans during propeller operation in the regime of constant speed and thebeta range, second valve means serially connected between said source offluid under pressure and said first valve means and operable to con- 12trol said pitch adjusting means during feathering operation of saidpropeller, said second valve means including a valve element having apair of interconnected cam followers for positioning the same, a pair ofindependently movable cams engageable with said cam followers, firstmeans operable to move one of said cams to position said valve elementand actuate the second valve means to initiate feathering operation ofsaid propeller, manually operable means for selecting the regime ofpropeller operation, and means operable during propeller operation inthe beta range to move the other cam and render said one cam inoperativeto position said valve element and thereby prevent actuation of thesecond valve means by operation of said first means.

3. The combination set forth in claim 2 wherein said pair ofinterconnected cam followers are mounted on a trolley, and wherein saidtrolley is pivotally connected to said valve element.

4. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure, a servo actuated distributor valve for controlling the flow offluid to and from said fluid pressure operated means during propelleroperation in the regimes of constant speed and the beta range, agovernor pilot valve connected between said source of fluid pressure andsaid servo actuated distributor valve for controlling the positionthereof, manually operable means to position said governor pilot valveto select any blade angle in the beta range during propeller operationin said beta range, feedback operated means connected with saidpropeller for repositioning said governor pilot valve when the selectedblade angle has been attained during operation in said beta range, afeathering valve serially connected between said source, said servoactuated distributor valve and said fluid pressure operated means, saidfeathering valve having a first position wherein it connects said sourceof fluid under pressure with said distributor valve and a secondposition wherein it interrupts the connection between said source andsaid distributor valve and establishes a direct connection between saidsource and said pitch adjusting means, first means operable to effectmovement of said feathering valve from said first position to saidsecond .position to initiate feathering operation of said propeller,manually operable means for selecting the regime of propeller operation,and means operable during propeller operation in the beta range forpreventing movement of said feathering valve from said first position tosaid second position by operation of said first means.

5. The combination set forth in claim 4 including spring means normallymaintaining said feathering valve in said first position, servo meansoperable to move said feathering valve to said second position, and atrigger valve connected between said source and said servo means forcontrolling the actuation thereof.

6. The combination set forth in claim 5 including a pair ofinterconnected cam followers for positioning said trigger valve, andwherein said first means comprise a first cam engageable with one ofsaid cam followers for positioning said trigger valve to interconnectsaid source and said servo means.

7. The combination set forth in claim 6 wherein the means operable toprevent actuation of the feathering valve by operation of said firstmeans during propeller operation in the beta range comprises a secondcam engageable with the other of said cam followers for rendering saidfirst cam inoperative to actuate said trigger valve.

8. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in beta. range.and feathering operation, the combination including, power operatedmeans for adjusting propeller, pitch, first control means operable tocontrol the pitch adjusting means during propeller 0poration in theregimes of constant speed and the beta range, second control meansserially connected with said first control means and said power operatedmeans and operable to control normal feathering operation of saidpropeller, first means operable to actuate said second control means toinitiate normal feathering operation of said propeller, manuallyoperable means for selecting the regime of propeller operation, andmeans operable during propeller operation in the beta range forpreventing actuation of said second control means by operation of saidfirst means.

9. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, pressure developing meansenergized incident to propeller rotation, first valve means forcontrolling the flow of fluid under pressure from said pressuredeveloping means to said pitch adjusting means during propelleroperation in the regimes of constant speed and the beta range, secondvalve means serially connected between said pressure developing means,said first valve means and said pitch adjusting means for controllingthe flow of fluid therebetween during normal feathering operation ofsaid propeller, a normal feathering control to actuate said second valvemeans to initiate normal feathering operation of said propeller,manually operable means for selecting the regime of propeller operation,and means operable during propeller operation in the beta range forpreventing actuation of said second valve means by operation of saidnormal feathering control.

10. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure energized incident to propeller rotation, first valve means forcontrolling the flow of fluid between said source of fluid underpressure and said pitch adjusting means during propeller operation inthe regimes of constant speed and the beta range, second valve meansserially connected between said source, said first valve means and saidpitch adjusting means, said second valve means having a first positionwherein it connects the source of fluid under pressure with said firstvalve means and a second position wherein it interrupts the connectionbetween said source and said first valve means and establishes a directconnection between said source and said pitch adjusting means to effectnormal feathering operation of said propeller, a normal featheringcontrol operable to move said second valve means from said firstposition to said second position, manually operable means for selectingthe regime of propeller operation, and means operable during propelleroperation in the beta range for disabling said normal featheringcontrol.

11. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure energized incident to propeller rotation, first valve means forcontrolling the flow of fluid between said source of fluid underpressure and said pitch adjusting means during propeller operation inthe regimes of constant speed and the beta range, second valve meansserially connected between said source, said first valve means and saidpitch adjusting means, said second valve means having a first positionwherein it connects the source of fluid under pressure with said firstvalve means and a second position wherein it interrupts the connectionbetween said source and said first valve means and establishes a directconnection between said source and said pitch adjusting means to effectnormal feathering operation of said propeller, a normal featheringcontrol operable to move said second valve means from said firstposition to said second position, and an emergency feathering controloperable to move said second valve means from said first position tosaid second position to initiate emergency feathering of said propeller.

12. The combination set forth in claim 11 including spring meansnormally maintaining said first valve means in said first position,servo means operable to move said second valve means to said secondposition, and a trigger valve connected between said source of fluidunder pressure and said servo means for controlling the actuationthereof.

13. The combination set forth in claim 12 including a pair ofinterconnected cam followers for positioning said trigger valve, andwherein said normal feathering control comprises a first cam engageablewith one of said cam followers for positioning said trigger valve,wherein said emergency feathering control comprises a second camengageable with the other of said cam followers for positioning saidtrigger valve.

14. In a variable pitch propeller having several regimes of propelleroperation including constant speed operation, operation in a beta range,and feathering operation, the combination including, fluid pressureoperated means for adjusting propeller pitch, a source of fluid underpressure, a servo actuated distributor valve for controlling the flow offluid between said source of fluid to pressure and said pitch adjustingmeans in the regimes of constant speed and the beta range, a governorpilot valve connected between said source of fluid under pressure andsaid servo actuated distributor valve for controlling the positionthereof, a feathering valve serially connected between said source, saiddistributor valve and said pitch adjusting means, said feathering valvehaving a first position wherein it connects said source with said servodistributor valve and a second position wherein it interrupts theconnection between said source and said distributor valve andestablishes a direct connection between said source and said pitchadjusting means for controlling the flow of fluid therebetween duringfeathering operation of said propeller, a normal feathering controloperable to move said feathering valve from said first position to saidsecond position to initiate normal feathering operation of saidpropeller, and an emergency feathering control operable to move saidfeathering valve from said first position to said second position andsimultaneously position said governor pilot valve so as to effectmovement of said distributor valve to a position calling for propellerfeathering whereby if the feathering valve fails to move from said firstposition to said second position upon actuation of the emergencyfeathering control said distributor valve will initiate emergencyfeathering operation of said propeller.

15. The combination set forth in claim 14 including first cam actuatedmeans for controlling the position of said governor pilot valve, secondcam actuated means for controlling the position of said featheringvalve, and wherein said emergency feathering control includesoperatively interconnected means for simultaneously operating said firstand second cam actuated means.

References Cited in the file of this patent UNITED STATES PATENTS HirschSept. 4, 1956

